Add support for the --jobs option to be specified without an

Add support for the --jobs option to be specified without an
argument, and also support -j as a short option. Since optparse
doesn't natively support options with non-required args, create an
insert_optional_args() function that inserts the required argument
into the args so that optparse is happy. The function inserts the
string True as a substitute for the argument that is required. This
string is later converted to the True constant when stored in
the emerge opts dict (similar to how normal boolean options are
stored). The PollScheduler and SequentialTaskQueue classes recognize
the meaning of the True constant to mean unlimited concurrent jobs.

svn path=/main/trunk/; revision=11261